[PATCH 1/4] mtd: spi-nor-core: Do not start or end writes at odd address in DTR mode

[Manorit Chawdhry]

From: Pratyush Yadav <p.yadav at ti.com>

On DTR capable flashes like Micron Xcella the writes cannot start or end
at an odd address in DTR mode. Extra 0xff bytes need to be prepended or
appended respectively to make sure both the start and end addresses are
even.

Signed-off-by: Pratyush Yadav <p.yadav at ti.com>
Reviewed-by: Vignesh Raghavendra <vigneshr at ti.com>
Signed-off-by: Apurva Nandan <a-nandan at ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr at ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry at ti.com>
---
 drivers/mtd/spi/spi-nor-core.c | 59 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 55 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index f86003ca8c06..2b000151c97d 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -1805,11 +1805,62 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
 		if (ret < 0)
 			return ret;
 #endif
+
 		write_enable(nor);
-		ret = nor->write(nor, addr, page_remain, buf + i);
-		if (ret < 0)
-			goto write_err;
-		written = ret;
+
+		/*
+		 * On DTR capable flashes like Micron Xcella the writes cannot
+		 * start or end at an odd address in DTR mode. So we need to
+		 * append or prepend extra 0xff bytes to make sure the start
+		 * address and end address are even.
+		 */
+		if (spi_nor_protocol_is_dtr(nor->write_proto) &&
+		    ((addr | page_remain) & 1)) {
+			u_char *tmp;
+			size_t extra_bytes = 0;
+
+			tmp = kmalloc(nor->page_size, 0);
+			if (!tmp) {
+				ret = -ENOMEM;
+				goto write_err;
+			}
+
+			/* Prepend a 0xff byte if the start address is odd. */
+			if (addr & 1) {
+				tmp[0] = 0xff;
+				memcpy(tmp + 1, buf + i, page_remain);
+				addr--;
+				page_remain++;
+				extra_bytes++;
+			} else {
+				memcpy(tmp, buf + i, page_remain);
+			}
+
+			/* Append a 0xff byte if the end address is odd. */
+			if ((addr + page_remain) & 1) {
+				tmp[page_remain + extra_bytes] = 0xff;
+				extra_bytes++;
+				page_remain++;
+			}
+
+			ret = nor->write(nor, addr, page_remain, tmp);
+
+			kfree(tmp);
+
+			if (ret < 0)
+				goto write_err;
+
+			/*
+			 * We write extra bytes but they are not part of the
+			 * original write.
+			 */
+			written = ret - extra_bytes;
+		} else {
+			ret = nor->write(nor, addr, page_remain, buf + i);
+			if (ret < 0)
+				goto write_err;
+			written = ret;
+		}
 
 		ret = spi_nor_wait_till_ready(nor);
 		if (ret)

-- 
2.43.2